Two projects will be undertaken to test the hypotheses that daily rhythms affect all metabolic processes in the visual cells, and that analogous rhythms in rods and cones are about one-half day out of phase. All experimental animals will first be entrained to a daily light-dark cycle (L:D 12:12). Eyes will then be removed and studied by microscopy and autoradiography at many intervals throughout the cycle. Manipulations during the dark perod will avoid the direct use of visible light. The diurnal pattern of RNA synthesis will be studied in receptors of frog and goldfish. Eyecups will be incubated under the conditions described by Hall et al. (J. Mol. Biol. 45, 397, 1969). The incubating solution will contain 2mCi/ml of 3H-Uridine. After one hr of incubation, eyes will be fixed and subsequently analyzed by autoradiography. Diurnal variation in the structure of rod and cone synaptic terminals in lizard, goldfish and mouse will also be studied. Statistical and morphometric methods will be applied to determine changes in the number of synaptic ribbons and the population of synaptic vesicles within the terminals of rods and cones, respectively.